Conventional blood constituent processing systems typically utilize a disposable flexible tubing network (including connected related devices) for withdrawing blood from a donor, processing the blood (for example, to separate a desired blood constituent) and then returning processed blood constituents to the patient or donor. Blood constituent processing systems may, for example, be of the type which pass blood through a constituent separating device so as to obtain concentrated blood plasma and/or platelet constituents while returning residual blood constituents to the donor or making them available for other uses. While some systems use a single needle for withdrawal and return (e.g., on a time muliplexed basis), others use a pair of needles--one for withdrawal and one for return.
In such blood processing systems, it is, of course, necessary that air be purged from the tubing network prior to connection to a human patient or donor. It would also be advantageous for air to be purged automatically (as by the execution of a suitable computer program which effects control over fluid pumps, valves, etc., operatively acting on the network after its installation in a host machine) to minimize the phlebotomist's tasks.
Until the present invention, one conventional purge procedure has been simply to pass a purge fluid (i.e., a saline solution) through the tubing network until the fluid is discharged from the distal end of the collection/return needles with the discharged fluid being collected in a suitable waste receptacle. The saline solution is discharged from the needles until the phlebotomist is satisfied that all air has been purged in the upstream tubing network. This is not only a messy and wasteful procedure, it also necessarily exposes the needle to a nonsterile atmosphere throughout the procedure.
It is also known to provide a single tubular needle with a frangible sheath including a porous biological filter of the type which is permeable to gas (e.g., air) yet hydrophobic and thus impermeable to liquid (e.g., saline solution and/or blood). While enclosing a single needle with a biological filter/sheath may be adequate for relatively simple tubing networks--that is, tubing networks having few, if any, branches and/or flow paths--such a conventional system is inadequate for a relatively complex tubing network having numerous branches and/or flow paths which must be purged of air prior to use. The possibility exists in complex tubing networks for multiple "pockets" of air to be interspersed with the saline purge liquid. Thus, once an advance column of purge liquid reaches the biological filter sheath, air entrained upstream will not be permitted to reach the filter (and thus be purged from the tubing network) since the advance liquid column will, in effect, "lock" further flow towards the filter due to its impermeability to liquid.
To alleviate this problem and thus ensure complete air purging, it has been prior practice to circulate saline in a portion of the tube set and then to simply remove the biological filter/sheath so as to permit remaining upstream columns of saline liquid (and thus the remaining pockets of entrained air) to be discharged from the needle. Accordingly, for all intents and purposes, there only one conventional method of removing remaining pockets of entrained air from a complex tubing network--that is, by simply allowing a sterile liquid (e.g., saline) to freely flow through the tubing network and be discharged from the needle for a time sufficient to ensure complete air purging.
Prolonged exposure of the collection/return needles to a nonsterile environment is, for obvious reasons, undesirable. Yet the prior practices described above tend to exacerbate potential contamination of the needle since exposure to a nonsterile environment occurs during much of the purging cycle--and may continue even thereafter if the patient/donor is not accessible for immediate attachment after the purge cycle is complete. While it is perhaps physically impossible to maintain the needles in a completely sterile environment prior to their percutaneous entry into a patient or donor, it is highly desirable to minimize the time during which the needles are exposed to a nonsterile environment.
The present invention simultaneously accomplishes such goals in a dual needle type of system by commonly enclosing the collection and return needles in a sterile housing that can also be used to facilitate the purging cycle. Thus, saline liquid during the purge cycle is permitted to flow serially through the needles and the common enclosure, the air being then collected (or purged) in the enclosure itself and/or in a separate air trap location of the tubing network.
Even a single needle set may include a similar needle housing to facilitate purging--albeit the return fluid path could then be via a valved tubing branch or the like rather than via second regularly used needle/tubing branch as in a dual needle system, or could be returned cyclically via the singular tubing path is sufficient saline storage is made available in the needle housing.
The tubing network including the collection/return needles, their common enclosure and blood constituent processing devices (e.g., blood filters, platelet separators, etc.) can thus be manufactured as a unitary disposable unit which can be connected to an automatic blood processing unit prior to use. Moreover, since the tubing network will remain "closed" during the purge sequence, the tubing network is particularly adapted for automated purging of air. Once all air has been purged from the tubing network, the phlebotomist may wait until the patient/donor is at hand and prepared before separating the collection and/or return needle(s) from their enclosure and intravenously connecting them. The enclosure thus not only facilitates purging, it also maintains the needle(s) in a sterile environment to minimize the time interval in which the needles are exposed to a nonsterile environment.
The advantages and objects briefly mentioned above, as well as others, will be more clearly understood after careful consideration is given to the detailed descriptions of exemplary embodiments of this invention which follow.